<article class="picture">

  <!--没有图片时展示进度条-->
  <mat-progress-spinner *ngIf="!fileItem"
                        class="example-margin" color="primary"
                        mode="indeterminate" [value]="0">
  </mat-progress-spinner>

  <!--有图片则展示图片-->
  <div class="picture-content" *ngIf="fileItem">
    <img [src]="fileItem.fileContent">
  </div>

</article>
